This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. There is compelling evidence from animal models and postmortem human brains of Parkinson's disease (PD) patients that striatal spine loss is a key neuropathological feature of PD. Knowing that striatal glutamatergic afferents target dendritic spines, these data appear difficult to reconcile with physiological studies showing overactivity of the corticostriatal glutamatergic system in rodent models of parkinsonism, and evidence for an increased expression of the vesicular glutamate transporter type I (vGluT1), a marker of cortical terminals, in the striatum of PD patients and MPTP-treated monkeys. In light of data from other brain regions suggesting a tight correlation between morphology and function of axo-spinous glutamatergic synapses, we undertook a detailed ultrastructural analysis of corticostriatal (vGluT1-positive) and thalamostriatal (vGluT2-positive) axo-spinous glutamatergic synapses using a 3D electron microscopic approach in normal and MPTP-treated monkeys. Three main conclusions can be drawn from this analysis: (1) The spines contacted by cortical vGluT1-containing terminals have a larger volume and harbor significantly larger post-synaptic densities (PSDs) than those contacted by vGluT2-immunoreactive thalamic boutons, (2) A subset of thalamic, but not cortical, terminals display a pattern of multisynaptic connectivity in normal and MPTP-treated monkeys and (3) Both cortical and thalamic axo-spinous synapses undergo ultrastructural changes (larger spine volume, larger PSDs, larger pre-synaptic terminal) indicative of increased synaptic activity in parkinsonian animals.